The present invention relates to pipe couplings, and more particularly to compression pipe couplings.
The pipe coupling of such compression type has been conventionally known, which comprises a hollow main body having two ends, at least one of the ends having an externally threaded portion and a tapered portion on its inner surface; a cap nut having an internally threaded portion engageable with the externally threaded portion of the main body and a pipe passing bore formed in the center of its top wall; and a metal sleeve provided on its outer surface with a tapered portion having a smaller angle of inclination than the tapered portion of the main body. Further, also conventionally known is a pipe coupling which includes a metal front sleeve provided with a sphero-concave portion formed in its rear end centrally thereof, and a metal rear sleeve disposed to the rear of the front sleeve and provided at its front end with a sphero-convex portion fittable in the concave portion of the front sleeve.
Throughout the specification and the appended claims, the term "front" refers to the forward side with respect to the direction of advance of a nut when it is tightened, and the term "rear" to the reverse side.
According to the foregoing conventional pipe couplings, when the fluids passing through the pipe are those which corrode metals, like hydrofluoric acid or acetic acid, the sleeve had to be made of an expensive special alloy so as to be corrosion resistant. Moreover, on firmly tightening the nut, the sleeve was caused to seize the portions of main body, nut or another sleeve, in contact therewith since it was made of metal.